Crayfish are very versatile flies. Try dead drifting them like you would a nymph (tight line or with an indicator), strip them, or slowly swing them through a tail out. I like a strip and pause retrieve, hopping them along the bottom. Fish often strike on the pause. I also like to tight line through a run. The best crayfish flies are weighted at the back so they look like a fleeing crayfish when stripped. If not weighted at the back, try placing a split shot about 6-8 inches up the leader for the same effect. Two of the best patterns are Mays full motion crayfish and Clouser crayfish (use a split shot with the Clouser pattern).